1. Field of the Invention
The present invention relates to a substrate inspection apparatus, a substrate inspection method, and a method of manufacturing a semiconductor device, with the objective of observing or inspecting, for example, a semiconductor pattern by use of an electron beam.
2. Related Background Art
Methods of inspecting defects in semiconductor patterns with the use of electron beams have recently been developed and are now in use. One such method, disclosed in Japanese Patent Laid-Open No. 7-24939 by way of example, involves generating a rectangular electron beam as a primary beam by electron irradiation means and irradiating the specimen therewith, then projecting an enlarged image of secondary electrons and backscattered electrons generated from the specimen surface, as a secondary beam, by mapping projection optical means and obtaining an image of the specimen surface indicative of changes in the shape/properties/potential of the specimen surface by an electron detection means such as an MCP detector. In addition to that method, another method has been proposed in Japanese Patent Laid-Open No. 11-132975, for example, by which the primary beam is deflected by a Wien filter so as to be incident on the specimen surface, and also a secondary beam is allowed to proceed through the same Wien filter and enters mapping optical projection means.
However, the inspection process disclosed in Japanese Patent Laid-Open No. 11-132975 for example has a problem in that, when the primary beam is shone onto the specimen, local differences in the charge state of the specimen surface will be created, depending on the shape and properties of the specimen surface or the layers in the vicinity thereof, and thus the inspection characteristics will deteriorate due to the resultant local differences in potential. This point will now be discussed with reference to the accompanying figures. Note that the same portions in the figures discussed below are denoted by the same reference numbers and description thereof is repeated only when necessary.
As shown in FIG. 27, if there are portions 202 and 204 of mutually different potentials in a surface layer of a specimen S, potential gradients that are not parallel to the surface of the specimen S are generated in regions RD1 and RD2 above the vicinity of boundary surfaces C1 and C2 between the portions 202 and 204. When the secondary beams that are emitted in the vicinity of the boundaries C1 and C2 are controlled by a secondary optical system of the inspection apparatus to form an image on a detection surface of the detector, these potential gradients will exert an unwanted deflection effect on the secondary beams, hindering appropriate imaging and causing distortion and contrast deterioration in the detected image. This phenomenon is particularly obvious in the inspection of interconnection patterns for large-scale integrated circuits (LSIs). This is because, in LSI interconnections, each portion 202 of FIG. 27 corresponds to e.g. an insulator of SiO2 or the like and the portion 204 corresponds to e.g. a conductor of tungsten (W) or the like, so the charging of each insulator during irradiation by an electron beam will create a large potential difference with respect to the conductor.
Occurrence of such local potential differences is not limited to boundary surfaces between different materials in mutual contact. For example, even if there are insulating portions 214 between the metal wiring 212 on the specimen S of an integrated circuit wafer, as shown in FIG. 28, if the primary beam irradiates with an incident energy (energy of electrons that are directly incident on the specimen S) that gives a total secondary electron emission ratio σ for each insulating portion 214 of 1 or more, the surface of the insulating portion 214 will be positively charged. Such incident energy is about 50 eV to 1 keV if the material of the insulating portion 214 is SiO2, by way of example. In such a case, local potential gradients that are not parallel to the surface of the specimen S are generated in the vicinity of a boundary 216 between the metal wiring 212 and the insulating portion 214. These potential gradients will exert an inappropriate deflection effect on secondary electrons emitted with a low emission energy of no more than a few eV from each of a point P2 within the metal wiring 212 in the vicinity of the boundary 216 and a point P4 within the insulating portion 214 in the vicinity of the boundary 216, before they are imaged on the MCP detector by the secondary optical system. This will make the trajectories of the secondary electrons deviate from electron beam trajectories TJIP2 and TJIP4 that are ideal for accurate mapping projection and curve as shown by trajectories TJRP6 and TJRP8. As a result, accurate imaging of the secondary beam is hindered, raising a problem in that the accuracy of defect detection is adversely affected by distortion and contrast deterioration of the detected image.
In general, the following three characteristics are mainly required of a detected image of a secondary beam, in order to improve the defect inspection capabilities when using electron beams:    1) Distortion must be small;    2) The S/N ratio (the ratio of electrons that contribute to the imaging to noise electrons that do not contribute to the imaging, within the secondary beam signal that arrives at the detector from the material that is the specimen surface) must be large; and    3) The contrast between different materials must be large.